Conventionally, containers made of steel are generally used as storage vessels for high-pressure gas.
However, steel storage vessels are heavy in weight, and much labor for movement, transport and the like is required.
For example, for automobiles using gaseous fuel, lighter-weight fuel storage vessels are required for the purpose of reducing vehicle weight in order to keep the fuel consumption amount low.
As storage vessels for high-pressure gas, instead of the conventional steel storage vessels, pressure vessels made of composite material in which liner material (vessel body) of plastic or metal is strengthened by reinforcing fibers, have come into use. High filling pressure and reduction in weight are realized by pressure vessels having this fiber-reinforced composite material.
In the process for manufacturing the pressure vessels having the fiber-reinforced composite material, there exists the filament winding method (hereinafter, referred to as “FW method”) as a representative method for winding the reinforcing fibers.
This method is a method for manufacturing a pressure vessel having fiber-reinforced composite material, which includes winding continuous reinforcing fibers impregnated with plastic onto liner material (a vessel body), and then curing the plastic.
Pressure vessels can be easily manufactured by adopting this FW method. However, in the case in which pressure vessels having, for example, a burst pressure (breakage pressure) of more than 65 MPa are manufactured, the rate of occurrence of the strength of the reinforcing fibers tends to decline. Consequently, it is necessary to thickly wind the reinforcing fibers as a countermeasure thereto, resulting in a problem of increased vessel weight.
Japanese Unexamined Patent Application, First Publication No. H8-285189 discloses a pressure vessel in which carbon fibers having a tensile strength of 5500 MPa or higher. In this pressure vessel, high-strength reinforcing fibers are used in order to obtain a high filling pressure. Japanese Unexamined Patent Application, First Publication No. H9-280496 discloses a vessel in which carbon fibers having an elastic modulus of 200 GPa to 350 GPa and a strength of 4.5 GPa to 10 GPa are used so as to seek higher performance.
Adequate burst pressure is obtained with the aforementioned conventional pressure vessels; however, other problems are engendered as described below.
With regard to the properties required for pressure vessels, not only burst properties are important, but also fatigue properties are important.
Particularly in the case of pressure vessels in which liner material (a vessel body) having metal such as aluminum is used, it is possible to impart compressive stress to the liner material by conducting autofrettage treatment at high pressure. It is possible to improve fatigue properties by conducting the autofrettage treatment so that this compressive stress is within the range of linear characteristics of the liner material. However, in the case in which the pressure vessel is designed with the emphasis on the compressive stress imparted to the liner material, burst pressure is lowered to less than needs. On the other hand, in the case in which the pressure vessel is designed with the emphasis on the burst pressure, the required compressive stress is not imparted. As a result, there is a problem that the used amount of the reinforcing fibers must be increased in order to realize a suitable pressure vessel, resulting in increasing the weight of the vessel and so on.